This invention relates to a novel process for preparing anthranylaldehyde derivatives
More particularly, it relates to a process for preparing anthranylaldehyde derivatives of following formula (I): ##STR2## wherein Z.sup.1 and Z.sup.2 are same or different each other and each represent a hydrogen atom, a halogen atom, a methyl group or a trifluoromethyl group, Z.sup.1 is attached to ortho position to the amino group and Z.sub.2 may be positioned at any of 3-, 4-, 5- and 6-positions.
Compounds of formula (I) are expected to be used in various organic reactions as they have an aldehyde group, and therefore, it is quite important to develop an advantageous process for preparing the same. Among compounds of formula (I) obtained by the process of the invention, N-(2,6-dichlorophenyl)anthranylaldehyde having following formula (II) is an important material for preparing o-(2,6-dichloroanilino)phenylacetic acid having formula (III) (hereinafter referred to as "Dichlofoenac"), known as an anti-inflammatory and analgesic agent. ##STR3##
Known processes for the production of compound (III) include, for instance, those disclosed in Japanese Pat. Nos. 42-23418, 44-27374, 44-27573 and 45-11295. None of these methods, however, involves the aldehyde (II) as the starting material. The applicant has already developed a process for preparing Dichlofenac by using the aldehyde (II) as the starting material in Japanese patent application Nos. 51-142430 and 52-112210.
Heretofore, very few reports may be found regarding process for preparing aldehydes of formula (I), particularly aldehyde (II), with an exception of Japanese Pat. No. 47-20220 wherein there are disclosed a method of reducing N-(2,6-dichlorophenyl)anthranylic acid, a method of oxidizing o-(2,6-dichloroanilino)benzyl alcohol and a method of reducing N-(2,6-dichlorophenyl)anthranylic halide. The Specification, however, discloses no yield of the aldehyde (II). ##STR4##
The inventors have tried to produce the desired compound (I) directly by the condensation reaction of o-halogenobenzaldehyde with an aniline derivative having following formula (IV) but failed to succeed. ##STR5## (wherein, Z.sup.1 and Z.sup.2 are as defined above).
After further studies, the inventors have found that a condensation product may be formed in good yield by using an o-halogenoaldehyde, the aldehyde group of which is protected with a specific group, and that the protected group may readily be converted to free aldehyde group with an acid.